直流配电网/微电网是应对高比例新能源接入和助推新型电力系统发展的一项关键技术，双向隔离DC/DC变换器是其中的关键电力电子装备。CLLC型双向隔离DC/DC变换器具备优异的软开关特性和双向功率传输性能，是其中双向隔离DC/DC变换器的理想选择。本文从直流配电网/微电网经济和安全稳定运行的需求出发，对CLLC变换器低成本高效率转换（无传感器同步整流）和高动态控制两大关键技术问题进行了深入研究，主要内容如下：首先，针对CLLC变换器动态分析缺乏有效工具的问题，提出了基于多模态统一等效电路的CLLC变换器相平面轨迹分析方法。给出了动态条件下的相平面轨迹分析，并解释了从频率变化到增益变化这一特性在动态上发生演变的机理，为CLLC变换器动态过程与动态性能的分析研究提供了有力的理论工具。然后，针对现有无传感器同步整流方法依赖于求解复杂数学模型，实施难度大的问题，提出了基于先验工况信息融合的自然无传感器同步整流方法（用于频率调制）和基于统计特征分析的简化无传感器同步整流方法（用于内移相调制）。在基于先验工况信息融合的自然无传感器同步整流中，通过将先验已知的变换器工况与推导出的最优参考工况匹配，从而绕过求解计算，直接以最优参考工况所需的同步整流驱动信号进行控制，不依赖方程组求解计算即可实现精确的无传感器同步整流。在基于统计特征分析的简化无传感器同步整流方法中，直接采用统计特征分析的方式对同步整流计算进行简化，避免了复杂且困难的数学演绎推导，将无传感器同步整流求解所需的联立14个非线性方程组简化为求解一个一元二次方程，计算过程大大简化。最后，针对CLLC变换器现有控制方法缺乏清晰的动态运行机理支撑，仅能对特定工况作动态性能优化、适用性差的问题，提出了基于相平面轨迹扩张/收缩极限检测的高动态恒流控制方法。利用相平面轨迹分析模型，深入分析了CLLC变换器的动态过程机理，指出由开关频率变化影响输出电流是一个多时间尺度的动态过程以及变换器的动态性能的极限对应于其相平面轨迹扩张和收缩的极限。进而，利用副边谐振电容电压峰值信息实现了相平面轨迹扩张/收缩极限检测，保证动态过程中，变换器能够实现接近理论极限的动态性能，且方法适用性强。相比最优整定的PI控制器，提出方法的响应时间缩短50%以上，且响应无过冲。
DC distribution network / DC microgrid technology is one of the key technologies to the construction of new power system. Bidirectional isolated DC/DC converter is one of the most important power electronics devices in DC microgrid applications. The CLLC converter is regarded as an ideal solution for DC microgrid applications because of its excellent soft-switching characteristics and bidirectional power transmission performance. Based on DC microgrid applications’ requirements of economic, safe and stable operation, this paper focuses its research on low cost high efficiency power conversion and high dynamic control of CLLC converters. First, for the problem that dynamic analysis in CLLC converters lacks effective analysis tools, a unified equivalent circuit based state trajectory analysis method is proposed for CLLC converters. With proposed state trajectory analysis method, a comprehensive dynamic state trajectory analysis is provided and the dynamic mechanism of switching frequency influencing voltage gain is clarified. The proposed unified equivalent circuit based state trajectory analysis method provides a powerful theoretical tool for the research of CLLC’s dynamic process and dynamic performance. Second, for the problem that existing sensorless synchronous rectification (SR) methods relay on solving complex time-domain mathematical model (causing difficult implementation), a prior working condition information fusion based natural sensorless SR method (for pules frequency modulation) and a statistical feature analysis based simplified sensorless SR method (for inner phase shift modulation) are proposed.In prior working condition information fusion based natural sensorless SR method, by matching the prior working condition information with derived optimal reference working condition, SR drive signal required in practical control is nearly the same as SR drive signal for derived optimal reference working condition. As a result, accurate sensorless SR can be realized without any calculation (natural sensorless SR).In statistical feature analysis based simplified sensorless SR method, the simplification of SR calculation is realized by statistical feature analysis, complex and difficult mathematical deduction process is avoided. In proposed method, accurate SR drive signal can be generated by only sloving a standard quadratic-root formula instead of solving 14 nonlinear equations in traditional methods. Calculation is dramatically reduced (in DSP chip of TMS320F28335, the time consumption of proposed method is only 8.67us).Finally, for the problem of high dynamic control, a trajectory expanding/shrinking limitation detection based high dynamic constant current control method is proposed. Based on the state trajectory model of CLLC converter, a comprehensive analysis about CLLC’s dynamic process and dynamic performance is proposed: the multi-time-scale dynamic process of the change of switching frequency’s influence on output current is analyzed; the relationship between the state trajectory and the limitation of CLLC dynamic performance is clarified. Based on the understanding of CLLC’s dynamic process and dynamic performance, the proposed method uses the maximum voltage of secondary side resonant capacitor to detect the trajectory expanding/shrinking limitation and control the converter accordingly. By this way, the converter can achieve a dynamic performance very close to its theoretical best dynamic performance. Compared to PI controller with best-tuned parameters, the response time of proposed method is reduced by more than 50%, and no overshoot occurs.
